DESCRIPTION (From the Applicant's Abstract): Glutamate is the major excitatory amino acid transmitter in the retina and therefore plays a very important role in both the health and processing of the retina. Previous studies have shown that elevated levels of glutamate can lead to neural death yet in mice which lack the major glutamate transporter (GLAST) the retinas appear normal and do not show signs of degeneration. Using in situ hybridization and single cell RT-PCR, the retina of GLAST-KO mice will be examined to determine if the expression of the glutamate transporters GLT-1 and EAAT5, which have also been localized to the retina, is increased in these animals. In addition, these same techniques will be applied to a well studied cell within the mammalian retina, the rod bipolar cell, to investigate the controvertial issue of glutamate expression on these cells. The rod bipolar cell is known to express the metabotropic glutamate receptor mGluR6. However, previous studies have been contradictory about the expression of ionotropic glutamate receptors on the rod bipolar cell. Immunoistochemical studies suggest that these receptors are indeed on the rod bipolar cell but electrophysiological techniques are unable to verify the existence of these receptors. Rod bipolar cells from the mouse retina will be labeled with the marker PKC and in situ hybridization will be carried out to localize what ionotropic glutamate receptors are present in these cells. If necessary, single cell RT-PCR will be used as a more sensitive method of measurement.